1. Field of the Invention
The present invention relates to an optical unit, an image pickup device using the optical unit, and an on-vehicle image display device using the image pickup device.
2. Description of the Related Art
In recent years, there have been proposed systems for detecting an object in proximity to a driver's own vehicle by use of a camera mounted onto the vehicle. For example, an image captured with an on-vehicle camera is subjected to image recognition processing to determine a pixel position of the object in proximity to the vehicle in the captured image. Information about the set position and angle of the on-vehicle camera and the view angle of a lens is then used to convert the pixel position of the object in proximity to the vehicle in the captured image into an actual physical position relative to the vehicle (e.g. a distance and direction from the driver's own vehicle to the target object).
Typically, the on-vehicle camera operates in an environment where moisture droplets tend to adhere to the lens. If droplets adhere to the lens, light is refracted by the droplets, which adversely affects the image captured by the on-vehicle camera. On-vehicle camera lens surfaces are generally coated with a water-repellent material to prevent water deposit (see Japanese Unexamined Patent Application Publication No. 05-232566). However, because of this water-repellent coating, droplets tend to adhere to the lens in a ball-like shape. These water droplets can significantly affect the image captured by the camera.
In contrast, if the lens surface is coated with a hydrophilic material, water covers the entire lens screen, thereby changing the lens' refractive index. This change in the refractive index causes the captured image to be blurred, and a proper image cannot be obtained.